Incorporation of short fibers, flocks, and pulps into mixtures of thermoplastic, thermoset, or crosslinkable polymers significantly alters the physical properties of such compositions which can enhance the performance properties of manufactured parts comprised solely or in-part of such compositions. The effect of the addition of such fibers will vary with the length, type and loading of these fibers. Fibers that have been employed include cotton, polyester, polyamide, polyaramide, PTFE, carbon, fiberglass, etc.
The physical dispersion of such fibers is frequently very difficult, often requiring extensive mixing in internal mixers, masticators, extruders, etc. Such extensive mixing breaks down the polymer (polymer chain breakage) effectively lowering the polymer's molecular weight, which is undesirable. There are numerous contributory causes for this dispersion difficulty: increasing surface area with decreasing fiber lengths, electrostatic build-up on many short fibers, moisture content, fiber treatments (if any, such as latexes, bonding agents, sizing, etc.). Clumping of short fibers aggravates this dispersion difficulty. Clumps must be broken up and the individual fibers ‘wetted-out’ by the polymer-containing compound in order for acceptable fiber dispersion to occur. Some fibers, such as highly fibrillated polyaramides, pose additional problems due to the irregularity of their surfaces.
The industry has attempted to address these problems by pre-blending difficult to disperse fibers with polymeric latexes, wetting agents, surfactants, oils, resins, etc., often as fiber ‘master batches,’ with limited success. The addition of partitioning agents such as silica can be somewhat effective in preventing fiber clumping, and conductive carbon blacks and some graphites are effective in dissipating electrostatic charges that build up during fiber processing.
However, a need continues to exist in the art for a fiber blend that will effectively disperse into a polymer composition with minimal mixing, while still imparting beneficial properties to the final product.